Interchangeable lens and interchangeable lens system

ABSTRACT

Disclosed is an interchangeable lens system which comprises an interchangeable lens and a camera. the interchangeable lens includes a driving circuit controlled by data transmitted from the camera to the lens such that it displaces a controlled member of the lens, a detection circuit for detecting a displacement of the driving circuit, and a correction circuit for converting the output characteristics of the detection circuit into predetermined common characteristics. The camera includes a control circuit for driving the driving circuit in the interchangeable lens in response to the output of the detection circuit in the interchangeable lens.

This is a continuation of prior application Ser. No. 08/111,266, filedAug. 24, 1993, abandoned; which is a continuation of prior applicationSer. No. 08/009,414, filed Jan. 27, 1993, abandoned; which is acontinuation of prior application Ser. No. 07/825,844, filed Jan. 24,1992, abandoned; which is a continuation of prior application Ser. No.07/533,683, filed Jun. 5, 1990, abandoned; which is a division of priorapplication Ser. No. 07/393,644, filed Aug. 14, 1989, now U.S. Pat. No.4,959,728.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an interchangeable lens and an interchangeablelens system of the type in which information is exchanged between thelens and a camera.

2. Description of the Related Art

In a conventional interchangeable lens system, a controlled system of alens unit is designed to have always the same configuration regardlessof the types of lens employed. Furthermore, variations in thecharacteristics of the individual controlled systems which occur duringthe mass production are coped with by sorting parts havingcharacteristics conforming to the standard.

However, the above-described conventional methods reduce mass productionyield because of strict standards, thereby decreasing productivity.Further, technical restrictions created when an old type lens isdesigned are imposed on the design of a new type lens, preventingoptimal design of the new type lens.

Further, in a conventional video camera, a diaphragm is controlled usingan aperture value detected in an operated state of the camera by asensor, such as a Hall element, provided at the diaphragm of the lens.

In the case of a video camera of the type in which a lens and a camerabody are formed as one unit, an aperture value detection signal istransmitted from the lens to the camera body in the form of an analogsignal.

In the case of a video camera of the type in which the lens can bedetached from the camera body, a detection signal is converted into adigital signal by an A/D converter, and the digital signal istransferred to the camera body.

However, the quantization level at which the detection signal isconverted into a digital signal may differ depending on thecharacteristics of the interchangeable lens employed, and this causesdetrimental effects on the compatibility of the interchangeable lenssystem.

Furthermore, an interchangeable lens system which is adapted to a VTR orthe like has its own exposure adjustment mechanism. This means that theexposure standard value of the lens, the dynamic range of an exposuresignal or the like generated by a control circuit of the camera bodyvary in a wide range depending on the type of the lens employed. Inconsequence, sufficient compatibility of the lens control informationcannot be ensured, this leading to the generation of automatic exposureadjustment errors.

In the control method in which digital communication is performedbetween a lens and a camera body, there is a possibility of delay incontrol or hunting.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an interchangeable lenssystem which is intended to eliminate the aforementioned problems of theprior art, which enables malfunctions of an interchangeable lens to beeliminated, and which ensures a high system extensibility.

In order to achieve the aforementioned object, the present inventionprovides in one form an interchangeable lens and an interchangeable lenssystem which includes correction means for correcting the output ofdetection means of a controlled system such that the virtual responsecharacteristic of the controlled system to a camera unit becomes apredetermined common function (e.g., linear).

In this way, a highly compatible interchangeable lens system, in whichcommon control can be performed regardless of the characteristics of thecontrolled system, can be provided.

In order to achieve the aforementioned object, the present inventionprovides in another form an interchangeable lens which comprises drivingmeans controlled by data transmitted from a camera body to the lens foroperating a controlled member of the lens, detection means for detectinga state of the driving means, and correction means for converting anoutput of the detection means into a signal representing either of aplurality of absolute, common regions.

The present invention provides in another form an interchangeable lenssystem which comprises: an interchangeable lens including detectionmeans for detecting a state of a controlled member of the lens andcorrection means for converting an output of the detection means into asignal representing either of a plurality of absolute, common regions;and a camera on which the interchangeable lens can be detachablymounted, the camera including control means for forming a control signalwhich controls the controlled member by photoelectrically converting animage received through the lens.

In this present invention, the output of the aperture value detectionsensor is corrected such that the virtual response characteristic of theaperture value detection sensor to the camera body becomes linear, andthis linear region is divided into fixed regions. In consequence, highlycompatible interchangeable lens and the interchangeable lens system, inwhich common control can be performed regardless of the characteristicsof the aperture value detection sensor, can be provided.

The present invention provides in another form an interchangeable lenssystem which comprises a camera unit and a lens unit that can bedetachably mounted on the camera unit. The camera unit includes exposurecontrol signal forming means for forming an exposed state control signalfor controlling an exposed state and a control reference value of theexposed state control signal, an encoder for converting the exposedstate control signal into coded data, and transmission means fortransmitting the coded data to the lens unit. The lens unit includescontrol means for controlling the exposed state on the basis of thecoded data received.

In this way, an optimal exposure adjustment operation is enabledregardless of the type of lens combined with the camera unit.

The present invention provides in another form an image sensingapparatus of the type in which an exposed state is feedback controlledon the basis of the output of image sensing means. The image sensingapparatus includes control means for varying the amount of feedbackaccording to a frequency of the changes in the output.

The present invention provides in another form an interchangeable lenssystem which comprises a camera unit and a lens unit that can bedetachably mounted on the camera unit. The camera unit includes exposurecontrol signal forming means for forming an exposed state control signalfor controlling an exposed state and a control reference value of theexposed state control signal, an encoder for converting the exposedstate control signal into coded data, and transmission means fortransmitting the coded data to the lens unit. The lens unit includescontrol means for controlling a transition process of the exposed stateon the basis of the coded data received.

In this way, hunting in the exposure control can be prevented. Further,an optimal exposure adjustment operation is enabled regardless of thetype of lens combined with the camera unit.

Other objects and features of the present invention will become moreapparent from the following description of the preferred embodimentsthereof, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a first embodiment of the presentinvention;

FIG. 2(A) shows an example of sensor input/output characteristics of thepresent invention;

FIG. 2(B) shows an example of division of a region;

FIG. 3 is a flowchart of the operation of a lens microcomputer;

FIG. 4 is a schematic view of a second embodiment of the presentinvention;

FIG. 5 is a flowchart of the operation executed in the second embodimentof the present invention;

FIG. 6 is a block diagram of part of a third embodiment of the presentinvention;

FIG. 7 shows an example of exposure control data employed in third andfourth embodiments of the present invention;

FIG. 8 is a flowchart of the operation executed in the embodiment shownin FIG. 6;

FIG. 9 illustrates a fourth embodiment of the present invention;

FIG. 10 is a flowchart of the operation executed in the fourthembodiment of the present invention;

FIG. 11 is a block diagram of the essential parts of an image sensingapparatus and an interchangeable lens system, showing a fifth embodimentof the present invention;

FIG. 12 is a flowchart of the operation executed by the system shown inFIG. 11;

FIGS. 13(A) and 13(B) are flowcharts of subroutines executed in theembodiment shown in FIG. 12; and

FIG. 14 is a flowchart of the operation executed by a camera unit,showing a sixth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a first embodiment of the present invention.

Diaphragm control in a video camera of the type in which a lens LS and acamera body CM can be separated from each other will be described below.

As image of an object (not shown) is formed on an image sensor 3 of thecamera body by an optical system 1 and an iris 2 of the lens.

An image signal representing the image formed on the image sensor 3 issupplied to a camera signal processing circuit 4. The camera signalprocessing circuit 4 produces a color signal C and a luminance signal Yas a video signal. The video signal passes through an encoder 5 thatemploys an NTSC method or the like, and is output from the camera bodyin the form of a composite video signal or the like.

Also, the luminance signal Y is supplied to an automatic exposure (AE)circuit 7 for generating an iris control signal in order to control theiris 2 according to the luminance of the picture such that correctexposure can be obtained.

More specifically, a portion of the luminance signal which represents apredetermined portion of the picture is extracted by a signal gatecircuit 6 which is controlled by a camera microcomputer 9, and theextracted portion of the luminance signal is supplied to the AE circuit7. The AE circuit 7 generates a control signal in order to control theiris 2 of the lens and thereby maintain the picture in a correctlyexposed state. The control signal generated by the AE circuit 7 isconverted into a digital signal by an A/D converter 8, and the resultantdigital signal is input to the camera microcomputer 9.

The camera microcomputer 9 transmits the digital control data to a lensmicrocomputer 10 through a connector CN that directly connects thecamera microcomputer 9 and the lens microcomputer 10. The control datatransmitted from the camera unit is converted into an analog signal by aD/A converter 11. The analog signal passes through a driving circuit 12and is then supplied to an actuator 13, which drives the iris 2.

The results of the driving is detected by an iris sensor 14. Thedetection signal of the iris sensor 14 passes through a sensor amplifier15, and the resultant signal is converted into a digital signal by anA/D converter 16. The digital signal is then input to thelens-microcomputer 10. The lens microcomputer 10 compares the digitalsignal and the control signal which is output to the D/A converter 11.The microcomputer 10 continues to drive the actuator 13 until thedesired results can be obtained.

In this way, a servo loop within the lens is formed, which monitorswhether the iris 2 is driven as is instructed by the control datatransmitted from the camera microcomputer 9.

Following has to be taken into consideration when this servo loop is tobe formed:

(1) variations in the characteristics of the individual sensors 14;

(2) differences in the characteristics which are determined by the typeof the sensor 14 or the detection method employed by the sensor 14;

(3) differences in the characteristics which are determined by the shapeor the structure of the iris 2, or the number of blades.

In order to achieve a sensor system which is capable of absorbing thedifferences in these characteristics and which has a virtually linearinput/output characteristic, a correction table 17 is employed in thisembodiment.

The correction table 17 is created as follows: First, the standardcharacteristics (such as those shown by "a" in FIG. 2(A)) are set, andthe difference between these standard characteristics and the datadetected by the sensor 14 (such as that shown by "b" in FIG. 2(A)) isthen obtained. This difference is written in the correction table 17 ascorrection data. The correction table 17 may be a memory such as EEPROM.

During the driving of the iris 2, the ROM table of the correction table17 is accessed by using the output of the A/D converter 16, which is thedata detected by the sensor 14, as an address to read out the correctionvalue stared beforehand, the correction value being then converted intothe standard characteristics.

The axis of ordinate in the characteristics conversion table shown inFIG. 2(A) represents the final output of the iris sensor system.

Furthermore, in this embodiment, the axis of ordinate is divided intoabsolute, common eight regions, which correspond to the individualaperture values.

FIG. 2(B) shows a concrete example of the eight-region division.

The axis of abscissa represents the F-number indicating the state of theiris.

For example, the output of the iris sensor may be divided into fixedregions in the manner described below.

1: F=1.4 or less

2: F=1.4 to 2.0

3: F=2.0 to 2.8

4. F=2.8 to 4.0

5: F=4.0 to 5.6

6. F=5.6 to 8.0

7: F=8.0 to 11.0

8: F=11.0 or above

Region division method of the present invention will be described indetail below using three lenses c, d, and e.

Both of the lenses c and d have a full-aperture F number of 1.8. In thecase of the lens c, the output of the iris sensor is divided into eightregions with the full-aperture F number being as the standard. In thecase of the lens d, the output of the iris sensor is divided into theeight fixed regions which are described above. The lens e has afull-aperture F number of 1.2, and it also employs the above-describedeight fixed region division.

As can be seen from the above description, the same region can be usedto denote the same states of the irises of the lenses having differentfull-aperture F numbers. This allows the camera unit to readily copewith different types of lenses.

The thus-obtained aperture information is employed in theabove-described servo loop. Alternatively, it may be transmitted to thecamera microcomputer 9 through the lens microcomputer 10, by means ofwhich a servo loop is formed for exposure control by the iris 2, theimage sensor 3, the camera signal processing circuit 4, the gate circuit6, the AE circuit 7, the A/D converter 8, the camera microcomputer 9,the lens microcomputer 10, the D/A converter 11, the driving circuit 12,and the actuator 13.

The control data transmitted from the camera microcomputer 9 may be datarepresenting the direction of drive of the aperture blades and datarepresenting the amount of drive thereof.

FIG. 3 is a flowchart of the operation of the microcomputer 10incorporated in the lens LS which is performed to form the former servoloop. First, in step #1, the microcomputer 10 receives the control datawhich is transmitted from the camera, and then sets "1" in the driveflag FL in step #2. Thereafter, in step #3, the microcomputer 9transmits the flag FL to the camera microcomputer 9, and then generatesin step #4 drive data Di on the basis of the data which has beenreceived from the camera in step #1. Next, in step #5, the microcomputer9 receives the data Si from the sensor 14, and then sets the address ofthe correction table 17 in step #6. Subsequently, in step #7, themicrocomputer 9 receives correction data Ci, operates Si * Ci=Ai toobtain data Ai used for data correction in step #8, then obtains thedifference Bi between data Ai and data Di in step #9. Execution of theprocessings from steps #4 to #9 is repeated until it is determined instep #10 that the difference Bi is 0. Once Bi has been 0, themicrocomputer 9 stops the drive in step #11, and then transmits flag FL"0" to the camera in step #12.

Next, a second embodiment of the present invention will be describedbelow with reference to FIGS. 4 and 5.

In this embodiment, the correction table contains two types of data, theone (i) representing variations in the characteristics determined by thetype of the lens, and the other (ii) representing variations in thecharacteristics of the individual products which occur during the massproduction.

Data (i) is stored in a correction table 18, and data (ii) is stored ina correction table 19.

Unlike the first embodiment in which the correction table stores data onthe basis of which correction is made, corrected data is stored in eachof the correction tables in the second embodiment. This simplifies thedata processing executed after the read-out of the ROM tables.

The two ROM tables are dependently connected with each other. So,read-out of the tables is performed as follows: As shown in theflowchart in FIG. 5, the correction table 18 is accessed using theoutput Si of the A/D converter 16 as an address in step #6-1, and thecorrected data Xi is then read out in step #7-1. Thereafter, thecorrection table 19 is accessed using the data Xi as an address in step#6-2, and the corrected data Yi is read out from the correction table 19in step #7-2. Next, in step #9', the difference Zi between the data Yiand the driving data Di is obtained, and then execution of theprocessings from steps #4 to #9' is repeated until it is determined instep #10' that the difference Zi is 0. In this way, lens designing canbe performed independently of the adjustment operations performed duringthe mass production. It is also possible to prepare a common ROM whichcan be used in various applications.

As will be understood from the foregoing description, it is possible toabsorb the variations in the characteristics of the individual lenseswhich occur during the mass production and changes in thecharacteristics which are determined by the types of the sensor or theoptical control mechanism which are employed in the lens unit. Inconsequence, predetermined procedures can be used by the camera unit tocontrol the lens unit even when different types of lenses are employed.This provides for an interchangeable lens system which can be handled bya simple operation. In the above-described embodiments, aperture controlhas been described. However, an auto focusing member, a zoom lens or ashutter may also be controlled in the same manner as that describedabove.

Furthermore, in the above-described embodiments, the output of theaperture value detection sensor is corrected such that the virtualresponse characteristics thereof become linear, and this linear outputregion is divided into a plurality of absolute, fixed regions. Inconsequence, it is possible to achieve a highly compatibleinterchangeable lens or interchangeable lens system in which a commoncontrol can be performed regardless of the characteristics of theaperture value detection sensor.

Next, a third embodiment of the present invention will be describedbelow with reference to FIGS. 6 to 8.

In this embodiment, the AE circuit 7 shown in FIGS. 1 and 4 has theconfiguration shown in FIG. 6.

In the AE circuit 7, the luminance signal Y is integrated by anintegrating circuit 71, and the resultant signal is amplified to apredetermined level by an amplifier 72. Thereafter, the output of theamplifier 72 is adjusted by a DC level shifting circuit 73 such that areference level represents the same voltage in the different types ofcameras.

FIG. 7 shows an example of the communication data which is set byadjusting the amplifier 72 and the DC level shifting circuit 73according to the luminance of the signal input to the AE circuit 7.

The control data shown in FIG. 7 is representative values of the controldata which are expressed in 8 bits (256 stages).

As shown in FIG. 7, the differences in level are expressed by exposurevalues (EV). For example, +1 EV means 1 EV (one aperture value)overexposure relative to the correct exposure, and that the iris in thelens unit should be closed by 1 EV.

Further, in this embodiment, a reference value for the exposure controlis set to "32". When this data is transmitted, driving of the iris 2 isnot performed.

The control data transmitted from the camera unit to the lens unit isconverted into an analog signal by the D/A converter 11, and the analogsignal is supplied to the actuator 13 through the driving circuit 12 todrive the actuator 13 and hence the iris 2.

Thus, in this embodiment, the exposure control signal including thestoppage of iris drive which is generated on the basis of the videosignal level as iris control information is converted into a digitalsignal, and the digital signal is transmitted to the lens unit. In thisway, the virtual difference in the gains within a camera can beneglected, and the difference in the dynamic ranges of cameras can alsobe neglected.

Furthermore, the reference value is expressed by a predetermined code,and this improves compatibility of the system.

In this embodiment, communication data is an 8-bit data. However, it mayalso be expressed by data having any number of bits. Further, thereference value may be any value other than 32.

Next, another example of the control operation in the interchangeablelens system shown in FIG. 1 will be described below with reference toFIG. 8.

First, the processing executed by the camera unit will be described.

Step #13: The output of the AE circuit 7 is received from the A/Dconverter 8

Step #14: Input of a video vertical synchronizing signal (Vsync) isawaited for a certain number of fields.

Step #15: A chip-select signal is set.

Step #16: Parallel iris data is converted into serial sequential irisdata, and the converted data is transmitted from the camera unit to thelens unit.

Step #17: The chip-select signal is reset. Next, the processing executedby the lens unit will be described.

Step #18: Input of the chip-select signal is confirmed.

Step #19: Serial sequential iris data is received as parallel data.

Step #20: The iris data received is sent to the D/A converter 11.

Thus, communication of the control data is performed between the cameraunit and the lens unit, whereby control is executed.

As will be clear from the foregoing description, even if any type ofinterchangeable lens is combined with the camera unit, the difference inthe characteristics of the exposure adjustment mechanisms can becompensated for without modifying the camera unit, enabling provision ofa highly reliable interchangeable lens system which ensures that theperformance of the exposure adjustment mechanisms which may differaccording to the types of lens employed is the same.

Next, a fourth embodiment of the present invention will be describedbelow with reference to FIGS. 9 and 10.

In the fourth embodiment, part of the AE circuit (71, 72 and 73)included in the third embodiment is incorporated in the cameramicrocomputer 9.

Whereas predetermined codes representing the iris control informationare generated by adjusting the bias and the amplification factor in thethird embodiment, a reference value is generated by a reference voltagegenerator 21 in the fourth embodiment, the generated reference valuebeing sent to the camera microcomputer 9 through an A/D converter 20.

The processing executed in the camera microcomputer 9 will be expressedas follows:

    Di=(Yc-Yb)/(Yr-Yb)×32                                (1)

where Di is iris data, Yc is the AE control signal input to the cameramicrocomputer 9, Yr is the Yc level at the reference level, and Yb isthe Yc level when no light falls on the imaging sensor. Yr level is setby the reference voltage generator 21, and the generated Yr level issent to the camera microcomputer 9 through the A/D converter 20.

Other processing is the same as that executed in the third embodiment.FIG. 10 is a flowchart of the operation executed in the fourthembodiment.

The processing executed in the camera unit will be described first.

Step #13: The output of the AE circuit 7 is received from the A/Dconverter 8.

Step #21: The reference level is received from the A/D converter 20.

Step #22: Iris data Di is operated.

Step #14: Input of a video vertical synchronizing signal (Vsync) isawaited for a certain number of fields.

Step #15: A chip-select signal is set.

Step #16: Parallel iris data is converted into serial sequential irisdata, and the converted data is transmitted from the camera unit to thelens unit.

Step #17: The chip-select signal is reset.

The lens microcomputer 10 executes the same processing as that shown inFIG. 8.

Thus, communication of the control information is performed between thecamera unit and the lens unit, whereby control is executed.

In the third and fourth embodiments of the present invention, the codesrepresenting the reference value and the exposure values which expressthe differences from this reference value are set beforehand, as shownin FIG. 7, and exposure control is performed by transmitting either ofthese codes. In this way, any type of interchangeable lens can be copedwith without modifying the structure of the camera unit.

In other words, it is possible to provide an extendable system which iscapable of coping with newly designed lenses without any problem, i.e.,it is possible to greatly increase the possibility of the systemexpansion.

Furthermore, since the processing of the reference value is performed bythe camera microcomputer, the initially adjusted values can be deletedand the possibility of the age deterioration can be decreased.

Next, a fifth embodiment of the present invention will be describedbelow.

In this embodiment, a history memory 9' which is accessed by the cameramicrocomputer 9 is incorporated in the fourth embodiment, as shown inFIG. 11. This memory stores the average value of the iris data over acertain period of time or a number of times inversion took place in theiris data over a certain period of time.

The camera microcomputer 9 performs the same processing as that shown inFIG. 10, and the lens microcomputer 10 executes the processing shown inFIG. 12, which includes:

Step #18: It is determined whether or not the chip-select signal isinput.

Step #19: Serial iris data is received as parallel data.

Step #23: The control value Di for a preceding few fields is read outfrom the history memory 9'.

Step #24: The subroutine shown in FIG. 13(A) is executed to calculatethe control data, that is,

Step #30: The number of times N that the sign of the control signalinverted in the predetermined number of preceding fields is counted.

Step #31: The feedback coefficient k is set according to N. In a casewhere the feedback coefficient k is large, it is set at a lower value sothat the response of the iris can be slowed down, so as to preventhunting.

Step #32: Operation of Di=Di k is executed to obtain iris control data.Thereafter, the processing returns to the main routine.

Step #25: The contents of the history memory 9' are renewed by the valuecalculated in step #24.

Step #20: The iris data is output through the D/A converter 11.

Thus, communication of control information is performed between thecamera unit and the lens unit, whereby iris control is performed.

Next, a sixth embodiment of the present invention will be describedbelow.

In this embodiment, operation of the control data (Di) which employs thehistory memory 9' is executed in the camera unit. This operation will bedescribed later with reference to the subroutine shown in FIG. 13(B).

The hardware structure and other processings are the same as those ofthe fifth embodiment.

In other words, the microcomputer 10 uses the same algorithm as thatshown in FIG. 8, and the microcomputer 9 employs the algorithm shown inFIG. 14.

First, the processing executed by the camera microcomputer will bedescribed.

Step #13: The output of the A/E circuit 7 is received through the A/Dconverter 8.

Step #21: The reference level is received through the A/D converter 20.

Step #22: The operation expressed by Equation (1) is executed to formthe iris data Di.

Step #23: The control data Di for a preceding few fields is read outfrom the history memory 9'.

Step #24: The subroutine shown in FIG. 13(B) is executed to calculatethe control data. That is:

Step #33: The difference "def" of the control signal Di in thepredetermined number of preceding fields is calculated. A vibrationperiod of the iris or a differential value of the changes in thevibration period may also be calculated on the basis of the obtaineddifference "def".

Step #34: The feedback coefficient k is set according to the differencevalue "def". In practice, in a case where "def" is large, the operationof the AE system may be stabilized by setting k to a smaller value sothat the response of the iris can be slowed down.

Step #35: The operation expressed by Di=Din * k is performed so as toobtain iris control data. Thereafter, the processing returns to the mainroutine.

Step #25: The contents of the history memory 9' are renewed by the valuecalculated in step #24.

Step #14: Input of a vertical synchronizing signal (Vsync) is awaitedfor a certain number of fields.

Step #15: A chip-select signal is set.

Step #16: Parallel iris data is converted into serial sequence data, andthe serial data is transmitted from the camera unit to the lens unit.

Step #17: The chip-select signal is reset.

Thus, communication of control data is performed between the camera unitand the lens unit, whereby iris control is performed.

In this data communication, a flag whose value indicates that theabove-described processing is performed in the camera unit or in thelens unit, i.e., a flag whose value indicates whether the datatransmitted from the camera unit to the lens unit is "processed data" or"raw data", may be set in the initial state (when power is turned on orwhen the lens is mounted) of communication, so that both types of datacan exist in one system.

The processings from steps #23 to #25 may be executed by the camera unitor the lens unit. Further more, the subroutines shown in FIGS. 13(A) and13(B) may be executed in either unit. Other algorithms that employ thehistory data of Di may also be used.

Furthermore, in the third, fourth, fifth and sixth embodiments, thecodes representing the reference value and the exposure values whichexpress the differences from this reference value are set beforehand, asshown in FIG. 7, and exposure control is performed by transmittingeither of these codes. In this way, any type of interchangeable lens canbe coped with without modifying the structure of the camera unit.

In other words, it is possible to provide an extendable system which iscapable of coping with newly designed lenses without any problem, i.e.,it is possible to greatly increase the possibility of the systemexpansion.

Furthermore, in the fifth and sixth embodiments, since the results ofthe analysis of the previous operations are utilized for the control,the response characteristic control of the system can be performed,which would be impossible in the conventional diaphragm control.

In particular, in a case where the control data is not transmitted fromthe camera unit for each field (e.g., in a case where the iris controldata is transmitted once for two fields), as in the fifth embodiment, ifthe history memory is incorporated in the camera unit, deterioration ofthe response of the system can be eliminated.

What is claimed is:
 1. An interchangeable lens system comprising:acamera unit and a lens unit that can be detachably mounted on saidcamera unit, wherein said camera unit includes exposure control signalforming means for forming a control reference value and an exposed statecontrol signal indicating a difference relative to said controlreference value on the basis of a common characteristic, an encoder forconverting said exposed state control signal into coded data, andtransmission means for transmitting said coded data to said lens unit,and wherein said lens unit includes control means for controlling theexposed state on the basis of the coded data received.
 2. An imagesensing apparatus of the type in which an exposed state is feedbackcontrolled on the basis of an output of an image sensing means,comprising feedback control means for varying the amount of feedbackaccording to a frequency of the changes in said output.
 3. An imagesensing apparatus according to claim 2, wherein said feedback controlmeans includes memory means for storing a frequency of changes in saidoutput of said image sensing means.
 4. An image sensing apparatusaccording to claim 2, wherein said feedback control means controls suchthat the amount of feedback is decreased when said frequency is large.5. An interchangeable lens system comprising:a camera unit and a lensunit that can be detachably mounted on said camera unit, wherein saidcamera unit includes exposure control signal forming means for forming acontrol reference value and and an exposed state control signalindicating a difference relative to said control reference value on thebasis of a common characteristic, an encoder for converting said exposedstate control signal into coded data, a memory for storing said codeddata, and transmission means for transmitting said coded data to saidlens unit, and wherein either said lens unit or said camera unitincludes operation means for reproducing and correcting a dynamiccharacteristic of an exposed state control signal by performing anoperation using said memory.
 6. An interchangeable lens system accordingto claim 5, wherein said memory stores an average value of said codeddata.
 7. An interchangeable lens system according to claim 5, whereinsaid memory stores a frequency of changes in said coded data.
 8. Asystem according to claim 7, wherein said memory is disposed at the sideof the camera, and said exposed state control signal corrected by saidoperating means is transmitted to said lens unit at a predeterminedperiod.
 9. A system according to claim 8, wherein said predeterminedperiod is V-sync.
 10. A video camera, comprising:a video camera unit,includinga) image sensing means for converting an incident light to animage signal; and b) exposure control means for outputting a controlsignal corresponding to a difference between a reference level and alevel of the image signal output from said image sensing means; and alens unit detachably mounted on said video camera unit, includingc) aniris; d) driving means for driving said iris; e) control means forcontrolling said driving means according to the control signaltransmitted from said video camera unit; and f) correcting means forcorrecting the control signal on the basis of a predetermined commoncharacteristic.
 11. A video camera according to claim 10, wherein saidcorrecting means is arranged to correct a linearity of a drivingcharacteristic of said iris.
 12. A video camera according to claim 11,wherein said lens unit further includes an iris encoder for detecting anoperating position of said iris and said control means is arranged tocontrol said driving means so that an iris value detected by said irisencoder becomes equal to an iris value indicated by the control signaltransmitted from the video camera unit.
 13. A video camera according toclaim 12, wherein said correcting means is arranged to correct an outputof said iris encoder.
 14. A video camera according to claim 10, furthercomprising transmission means, said transmission means being arrangedbetween said video camera and said lens unit to transmit an informationin synchronism with the V-sync and the information being transmitted bysaid transmission means.
 15. A video camera according to claim 10,wherein said correcting means further includes a memory in which errorinformation for said predetermined common characteristic of said controlsignal is stored.
 16. A video camera according to claim 15, wherein saidmemory stores the error information concerning the iris controlcharacteristic caused by the kinds of lens and the irregularities of thecharacteristic at the time of manufacturing.
 17. A lens unit detachablymounted on a video camera, comprising:a) an actuator for varying anoptical state of said lens unit; b) control means for controlling saidactuator according to a control signal transmitted from said videocamera; c) memory means for storing correction data for correcting anerror between the control signal relative to a predetermined commoncharacteristic; and d) correcting means for correcting an operation ofsaid control means according to the correction data read out from saidmemory means so that said actuator is controlled on the basis of saidpredetermined common characteristic.
 18. A lens unit according to claim17, wherein said actuator is arranged to drive an iris.
 19. A lens unitaccording to claim 18, wherein said correcting means is arranged tocorrect a linearity of a driving characteristic of said iris.
 20. A lensunit according to claim 19, wherein said lens unit further includes aniris encoder for detecting an operating position of said iris and saidcontrol means is arranged to control driving means so that an iris valuedetected by said iris encoder becomes equal to an iris value indicatedby the control signal transmitted from the camera unit.
 21. A lens unitaccording to claim 20, wherein said correcting means is arranged tocorrect an output of said iris encoder.
 22. A lens unit according toclaim 17, further comprising transmission means, said transmission meansbeing arranged between said video camera and said lens unit to transmitinformation in synchronism with the V-sync and the information beingtransmitted by said transmission means.
 23. An image processingapparatus, comprising:a) image sensing means for converting an incidentlight to an image signal; b) an actuator for varying an optical state ofsaid apparatus; c) control means for outputting a control signalcorresponding to a difference between a reference level and a level ofthe image signal output from said image sensing means and controllingsaid actuator on the basis of the control means; d) memory means forstoring information concerning a plurality of the control signals whichhad been previously output from said control means; and e) correctiondata for correcting the control signal on the basis of said informationstored in said memory means.
 24. An apparatus according to claim 23,wherein said information is an average value of said plurality of thecontrol signals.
 25. An apparatus according to claim 23, wherein saidinformation is a frequency of changes in the control signal.
 26. A lensunit according to claim 23, wherein said actuator is arranged to drivean iris.